It is known that hydrogen sulfide contained in gas mixtures can be catalytically reacted with sulfur dioxide in the Claus process to produce sulfur (Opened German Specification-Offenlegungsschrift-DT-OS 2,253,806corresponding to U.S. Pat. No. 3,896,215).
It is also known to cause the resulting exhaust gases to flow over an activated-carbon adsorbent at elevated temperatures to form elementary sulfur. The laden activated carbon can be regenerated by a treatment at temperatures of 350.degree. to 550.degree. C with an inert gas which is virtually free from oxygen, carbon dioxide, and water (German Pat. No. 1,667,636).
It has also been suggested to use alumina, which may be impregnated, if desired, or mixtures of alumina and silica, rather than activated carbon as an adsorbent. In that case the time of contact of the exhaust gas to be desulfurized is maintained between 1 and 25 seconds and the adsorbent is subsequently regenerated by a treatment with oxygen-free gas at temperature between 200.degree. and 350.degree. C (Opened German Specification (Offenlegungsschrift) DT-OS 2,319,532).
A process of lowering the content of combined sulfur in Claus process exhaust gases has been proposed in which the Claus process exhaust gases are cooled and the sulfur is condensed, the resulting gas, which is substantially free from elementary sulfur, is catalytically reacted to produce sulfur, the flow of gas into the catalyst bed is stopped when the degree of conversion has decreased, and a hydrogen-sulfide-containing gas at temperatures above the dewpoint of sulfur is passed through the catalyst bed to evaporate elementary sulfur from said bed until the activity of the catalyst has been restored (Opened German Specification Offenlegungsschrift - DT-OS 2,021,111).
Claus process exhaust gas or another H.sub.2 S-containing gas is used as a desorption gas in that process, in which the H.sub.2 S contents are relatively high and may be as high as 50% by volume. That process requires a special control of the gaseous constituents to be reacted and an exact supervision.
Specifically, the separate heating of the regenerating gas creates high energy requirements. Another disadvantage is that the recycling of the H.sub.2 S-reducing gas to the Claus process plant requires a high pressure and a separate gas blower.
Those known processes must be carried out in a plurality of stages, as a rule. For instance, the process according to German Pat. No. 1,667,636 comprises a first stage in which sulfur is formed in the presence of activated carbon, and a succeeding stage, in which the H.sub.2 S-containing gas, to which oxygen-containing gas has been added, is reacted to produce sulfur also in the presence of activated carbon.
In the process according to Opened German Specification No. 2,319,532 the regenerated adsorbent is purged at a temperature below 180.degree. C with oxygen-free gas and the purge gas contains added water vapor at least during part of the purging operation.